Antenna amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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The antenna amplifier brought to the attention of readers is designed to amplify the signals of broadcasting and television stations in the meter range.
Main technical characteristics of the amplifier
Bandwidth. MHz. when the signal is weakened at the edges of the range 3, dB....50...350
Self-noise level, dB....3,5
Input impedance, Ohm....75
Rated load resistance, Ohm....75
Voltage gain with an input signal of 5 μV, dB, at a frequency, MHz:
48 .... 39
230 .... 41
Schematic diagram of the amplifier is given in the figure. It is assembled on four transistors connected according to a common emitter circuit. A feature of the amplifier is the use of inductors as collector loads of transistors V3-V5, which reduced the blockage of the amplitude-frequency characteristic (AFC) of the amplifier at higher frequencies.
(click to enlarge)
The amplifier remains operational when the supply voltage drops to 4 V. In this case, the gain in the entire frequency range decreases to 36 dB. To operate the amplifier at a low supply voltage, the D814A zener diode must be replaced with a KS139A or KS147A. The current drawn from the power supply will drop to 15 mA in this case.
The amplifier is mounted on four boards with dimensions of 25x40 mm made of double-sided foil fiberglass 2 mm thick. One side of the board is used as a screen. The boards are installed in rectangular recesses of the brass case and are separated from each other by shielding partitions soldered directly to the foil surface of the boards.
Coils L1, L2, L4 contain 2,5 each, and L3 - 4 turns of PEL 1,0 wire. The winding diameter of coils L1-L3 is 12, and L4 is 20 mm. Winding step - 8 mm.
The adjustment of the amplifier begins with the setting of the DC transistor modes in accordance with those indicated on its diagram. Then proceed to the adjustment of the frequency response. To do this, you can use the devices X1-19A, X1-1. TR-0813 or GKCh of any type.
On GKCh set the selected frequency range at the maximum swing band. A voltage of 5 μV is applied to the input of the amplifier (such a signal corresponds to an attenuation of 1 dB on the X19-50A device). Setting up the amplifier is reduced to selecting the locations of the taps from the coils L1-L4 until the required transmission pass is obtained. The frequency response can also be measured using a calibrated standard signal generator and a tube voltmeter, shunting the latter with a 75 Ohm resistor (see the article by I. Genshenz, V. Kolomiets and N. Savenko "Antenna amplifier with remote tuning" in "Radio", 1975, No. 4, pp. 15, 16).
Authors: Yu. Bigeldin, A. Danilov, Ch. Seitnepesov, Ashgabat; Publication: N. Bolshakov, rf.atnn.ru
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